Centrifugal compressor



Oct. 31, 19G? H. w. KlRTLAND ETAL 3,349,999

CENTRIFUGAL COMPRESSOR Filed Sept. 1, 1965 2 Sheets-Sheet 1 FIG.|

v 1 J I j I Z j 21 1 INVENTORS.

HOWARD W. KIRTLAND. JAMES W. ENDRESS.

ATTORNEY.

Oct. 31, 1967 Fil ed- Sept. 1, 1965 H. w. KIRTLAND TAL CENTRIFUGAL COMPRESSOR FIG. 2

HOWARD JAMES 2 Sheets-Sheet 2 INVENTORS. W. KIRTLAND. W. ENDRESS.

ATTORNEY.

United States Patent 3,349,999 CENTRHFUGAL COMPRESSOR Howard W. Kirtland, East Syracuse, and James W.

Endress, Syracuse, N.Y., assignors to Carrier Corporafion, Syracuse, N.Y., a corporation of Delaware Filed Sept. 1, 1965, Ser. No. 484,399 5 Claims. (Cl. 230132) ABSTRACT OF THE DISCLOSURE An arrangement for relieving high pressure gas collecting in the space behind the impeller of a gas compressor while minimizing or preventing flow of lubricant into the space by employing openings in the impeller causing the impeller to apply pressure in the space sufficient to discourage the lubricant flow.

This invention relates to a centrifugal compressor and, more particularly, to a centrifugal refrigerant compressor and provision for substantially preventing undesirable leakage and mixing of lubricant and refrigerant in the compressor, and for reducing thrust on the compressor rotor assembly.

It is common practice in centrifugal refrigerant compressors to reduce thrust of the impeller by sealing 015? a portion of the rear side of the impeller and venting to a low pressure compressor inlet any high pressure refrigerant vapor which passes the seal and collects between the rear side of the impeller and compressor housing. A problem is that of lubricant for the compressor bearings passing along the impeller shaft to the sealed off portion of the impeller from which it may enter the refrigerant circuit and be deposited, thus reducing heat transfer of related equipment and requiring servicing of the equipment.

It is a primary object of this invention to provide a new and improved centrifugal compressor and, more particularly, to provision of low thrust loading on the compressor impeller while substantially preventing leakage of lubricant into the refrigerant circuit and leakage of refrigerant into the lubrication system.

These and other objects and advantages of the invention will be apparent from the following description and drawings, in which:

FIGURE 1 is a schematic flow diagram in section of a refrigeration system including a centrifugal refrigerant compressor with parts broken away for clearer illustration; and

FIGURE 2 is a schematic, fragmentary vertical axial sectional view of a lower portion of the refrigerant compressor.

With reference to FIGURE 1 of the drawing, a prime mover such as an electric motor 11 drives a centrifugal refrigerant compressor 12 from which compressed refrigerant vapor at a relatively high outlet discharge pressure passes through a compressor outlet of a compressor discharge 13 and then a hot gas line 14 to a refrigerant condenser 15 in which the gas is condensed. Liquid refrigerant from the condenser 15 is circulated through a metering device 16 to an evaporator 17 where it vaporizes and is withdrawn through a suction line 18 to a compressor inlet 19 at a relatively lower pressure than the discharge 13. A lubricant pump 20 in a lubricant line 22 circulates lubricant through the line from a lubricant reservoir 21 to the compressor 12. After l ubricating the compressor, most of this lubricant flows through a return line 23 back to the reservoir 21. The reservoir is illustrated as vented at 24 to the atmosphere. Refrigerant and lubricant mixed in the compressor 12 passes through conduit means including a drain line 25 to a Patented Oct. 31, 1967 suitable separator 26 from which the lubricant may be returned to the reservoir 21 by opening a normally closed shut-off valve 27 in a line 28 between the separator 26 and the reservoir 21. The refrigerant vapor is withdrawn through a refrigerant return line 29 to the compressor inlet portion 19. A suitable heater 30 immersed in the lubricant in the separator 26 may be used to drive off refrigerant absorbed by the lubricant.

With reference to FIGURE 2, the compressor 12 includes a housing 31 and therein a rotor assembly 32 including an impeller or wheel 33 suitably mounted on an end of a compressor drive shaft 34 for rotation therewith. The opposite end of the shaft '34 has suitable coupling means drivingly connecting the shaft with the motor 11. The shaft 34 is suitably mounted for rotation and held against axial movement in the housing 31 by bearing means including an inner rotary bearing 36 and an outer rotary bearing 37, and a thrust bearing assembly 38. The inner and outer bearings 36 and 37, respectively, are illustrated as sleeve bearings suitably fixedly seated in the housing 31', and the shaft 34 is in rotary engagement with these hearings. The thrust bearing assembly 38 is outward of the bearing 37 and includes a thrust disc 39 suit-ably fixedly mounted on the shaft 34 in bearing engagement with a thrust bearing 40 suitably fixedly seated on the housing 31.

Lubricant for lubricating the bearings passes from the lubricant supply line 22 to suitable passages associated with the housing 31 and including a pipe 41 interior of the housing and opening into a housing passage 42 communicating with a lubricant receiving chamber 43 in the housing. Lubricant from the bearings passes into a chamber 44 in a rear portion of the housing 31 and then passes through the return line 23 to the lubricant reservoir 21.

The inlet portion 19 of the compressor 12 is generally coaxial with the axis of rotation of the compressor shaft 34 and includes an inlet port 45 in the housing 31 and a front or inlet end 46 of the impeller 33. Cooling capacity of the system may be regulated by any suitable manner, for example, by guide vanes 47 in the housing inlet port 45 which may be suitably automatically adjusted responsive to the temperature of chilled water leaving the evaporator 17. The discharge portion 13 of the compressor 12 includes a tip portion 49 of the impeller 33. The tip portion 49 communicates through an annular passage 50 with a scroll diffuser 51 and then the compressor outlet to complete the discharge portion. The impeller 33 compresses refrigerant vapor from the inlet port 45 at a relatively low suction pressure to a relatively higher discharge pressure at the impeller tip 49.

A rear face 52 of the impeller 33 opposite the impeller inlet 46 is spaced from an adjacent face 53 of the housing 31 and therewith defines an annular gap 54 having an inner portion 54a and an outer portion 54b in direct communication at the rear of the impeller tip 49 with the annular passage 50, resulting in refrigerant vapor at impeller tip discharge pressure passing into the outer gap portion 54b. Between the inner and outer portions of the gap 54, the rear face 52 of the impeller 33 has cylindrical shoulder 55 which cooperates with an annular first or outer labyrinth 56 fixedly seated on the housing 31 for retarding flow of refrigerant into the inner gap portion 54a and toward the shaft 34. An annular second or inner labyrinth 57 cooperates with the shaft 34 and is suitably seated on the housing 31 for further retarding the flow of refrigerant from the inner gap portion 54a into a collection chamber 58 in the housing from which fluids are withdrawn through the drain line 25. The inner labyrinth 57 is between the gap 54 and the collection chamber 58.

An undesirably high thrust load acting on the impeller 33 and thrust bearing assembly 38 in a direction toward the inlet port 45 could result from relatively high pressure acting on the rear face 52 of the impeller and opposed only by the relatively lower force of the suction pressure in the inlet portion 19. To eliminate such objectionable high pressure the inner gap portion 54a may be vented to the inlet portion 19 of the compressor by passages 59 in the impeller 33 between the inner gap portion 54a and the inlet portion 19. The passages 59 are substantially equally spaced in a hub 60 of the impeller and are generally concentric about the shaft 34. These passages have inclined portions 61 converging relative to the axis of the shaft 34 from rear end portions 62 opening into the inner gap portion 54a to front end portions 63 communicating with the inlet portion 19 of the compressor. The passages are preferably inclined to maintain a pressure in the gap 54 adjacent the shaft 34 slightly above suction ressure to assure the flow of some refrigerant past the inner labyrinth 57 and into the collection chamber 58, as discussed later.

A seal assembly 64 for retarding leakage of lubricant from the lubricant receiving chamber 43 toward the impeller 33 includes a rotating seal ring 65 suitably keyed to the shaft 34 to rotate therewith and held against axial movement away from the inlet port 45 by a nut 66 threaded on the shaft. A suitable free sealing member, such as a carbon ring 67 or the like, is suitably mounted in spaced relationship with the shaft 34 and has opposite annular faces seated on the rotating seal ring 65 and on an annular shoulder of a non-rotating sleeve seal 68 about the shaft and non-rotatably seated on the housing 31. The non-rotating sleeve seal 68 is arranged to move only axially with respect to the shaft and is spring-urged away from the inlet port 45 by a non-rotating annular spring retainer assembly 69 and into sealing engagement with the free sealing member 67, and urges the free sealing member into sealing engagement with the rotating seal ring 65. The seal assembly 64 is more fully described in US. Letters Patent 3,035,841, granted May 22, 1962, to R. A. Riester for Compensating Seals, and reference may be had thereto if a more comprehensive description of this seal structure is desired. Any lubricant which passes the seal assembly 64 enters the collection chamber 58.

The collection chamber 58 is maintained slightly above suction pressure but below gap pressure by conduit means between the chamber and the compressor inlet portion 19 and including the drain line 25, separator 26, and the refrigerant vapor return line 29 from the separator to the inlet portion 19. Thus, the separator 26 is at substantially suction pressure except for line drops and a slight drop through a lubricant mist eliminator 70. By maintaining the gap 54 slightly above the collection chamber pressure, fio-w of refrigerant from the gap 54 into the chamber 58 is assured, thus substantially preventing passage of lubricant from the seal assembly 64 into the gap for possible passage into the refrigerant circuit. Any suitable seal, such as a chevron seal 71, may be provided between the shaft and the impeller for preventing the flow of refrigerant therebetween and into the compressor inlet portion.

To summarize the operation, when the compressor 12 is operating, refrigerant vapor is compressed by the impeller 33 from the relatively low suction pressure to the relatively higher discharge pressures and high pressure refrigerant passing into the gap 54 between the rear surface 52 of the impeller and the housing has its pressure reduced as it flows past the outer labyrinth 56 into the inner gap portion 54a and then through the passages 59 in the impeller to the compressor inlet portion 19. The inclined portions 61 of the passages 59 converge from the inner gap portion 54a to the inlet portion 19 of the comressor and the resultant centrifugal force of the refrigerant in these inclined portions maintains a refrigerant vapor pressure in the gap slightly above the suction pressure, thus maintaining a low thrust load on the rotor assembly 32. This pressure in the inner gap portion 54a is sufficient to cause slight flow of refrigerant from the gap past the inner labyrinth 57 and into the collection chamber 58 which is just slightly above suction pressure but below gap pressure. Any lubricant passing the seal assembly 64 enters the collection chamber 58 and is prevented from passing the inner labyrinth 57 and entering the gap 54 because of higher pressure in the inner gap portion and the resultant flow of refrigerant vapor from the gap past the labyrinth into the collection chamber. From the collection chamber 58 refrigerant and lubricant are removed through the drain line 25 and pass to the separator 26 where the lubricant collects in a lower portion of the separator and may be removed as desired by opening the shut-off valve 27. Refrigerant vapor in the separator 26 passes through the oil mist eliminator 70 and the refrigerant return line 29 to the inlet portion 19 of the compressor 12. The immersion heater 30 in a separator 26 may be used for driving any absorbed refrigerant from the lubricant.

While a preferred embodiment of the invention has been described and illustrated, it should be understood that the invention is not limited thereto but may be otherwise embodied within the scope of the following claims.

We claim:

1. A centrifugal compressor comprising a housing having inlet and outlet portions for the passage of refrigerant vapor through the compressor, an impeller in said housing for compressing refrigerant vapor from a relatively low suction pressure at said inlet portion to a relatively higher pressure at said discharge portion during operation of the compressor, bearing means mounting said impeller for rotation during operation of said compressor and mounting said impeller spaced from a portion of said housing to define a gap in direct communication with said discharge portion, whereby refrigerant vapor at said higher pressure passes into said gap, means for retarding flow of said refrigerant to at least a portion of said gap, means for providing lubricant to said bearing means at a pressure normally above said suction pressure, means providing a collection chamber in said housing between and in fluid communication with said gap and said hearing means, conduit means between said chamber and a separate chamber for maintaining said chamber at a pressure below said lubricant pressure during operation of the compressor, and means communicating with said inlet for maintaining a pressure in said gap below said higher pressure to reduce the thrust force on said impeller, and above the pressure in said collection chamber for assuring flow of refrigerant from said gap into said chamber and substantially preventing leakage of said lubricant into said gap, whereby refrigerant may flow from said gap into said chamber and lubricant may flow from said bearing means into said chamber.

2. The compressor of claim 1 in which the last said means defines a passage in said impeller converging relative to the axis of rotation of said impeller from an end of said passage opening into said gap to an opposite end opening into said inlet portion.

3. A centrifugal compressor comprising a housing having inlet and outlet portions for the passage of refrigerant vapor through the compressor, a rotor assembly in said housing and including a shaft and an impeller on an end of said shaft for compressing refrigerant vapor from a relatively low suction pressure at said inlet portion to a relatively higher pressure at said discharge portion during operation of the compressor, bearing means along said shaft mounting said rotor assembly for rotation in said housing during operation of said compressor and mounting said impeller spaced from a portion of said housing to define a gap in direct communication with said discharge portion, whereby refrigerant vapor at said higher pressure passes into said gap, flow retarding means in said gap for retarding flow of said refrigerant to an inner portion of said gap about said shaft, lubricating means for providing lubricant to said bearing means at a pressure normally above said suction pressure, means providing a collection chamber in said housing about said shaft between and in fluid communication along said shaft with the gap inner portion and said lubricating means, conduit means between said chamber and a separator chamber for maintaining said chamber at a pressure below the lubricant pressure and the pressure in said gap inner portion during operation of the compressor, whereby refrigerant may flow from said gap inner portion into said chamber and lubricant may flow from said lubricating means into said chamber, and means for maintaining a pressure in said gap inner portion below said higher pressure to reduce the thrust force on said shaft, and above the pressure in said collection chamber for assuring flow of refrigerant from said gap inner portion into said chamber and substantially preventing leakage of said lubricant along said shaft into said gap, the last said means defining a passage in said impeller converging relative to the shaft axis from an end of said passage opening into said gap inner portion to an opposite end opening into said inlet portion of the compressor.

4. In a gas compressor including a housing and a power shaft; an impeller rotatably mounted on the shaft within the housing for axially receiving gas at low pressure and for radially discharging same at a higher pressure; means including stationary and movable parts requiring lubrication mounted on said shaft; a lubrication system for supplying lubricant under pressure to the lubrication re- 30 quiring means, the lubrication system communicating in part with the low pressure side of the compressor; means forming a chamber having communication with the low pressure side of the compressor for receiving lubricant flowing from the means; the impeller being mounted relative to the housing to define a gap between the rearward side of the impeller and the housing, restriction means arranged in said gap to provide a radially outward portion communicating with the high pressure gas discharged 5 from said impeller and a radially inward portion communicating with the chamber receiving lubricant flowing from the lubricant requiring means, and means associated with the impeller and communicating with the low pressure side of the compressor for maintaining pressure on the inward portion of the gap at a magnitude less than the pressure in the outward portion of the gap to reduce the thrust load on the machine while maintaining pressure in excess of that in the chamber to discourage flow of lubricant into the inward section of the gap.

5. The invention set forth in claim 4 wherein said last mentioned means includes at least one opening inclined relative to the axis of the power shaft extending through the impeller, said opening being effective to supply refrigerant vapor under pressure to the inward portion of the References Cited UNITED STATES PATENTS 1,180,602 4/1916 Pfau 103112 1,473,802 11/1923 Woock et a1. 103112 FOREIGN PATENTS 179,275 12/ 1953 Austria. 564,319 10/1923 France. 924,068 2/1955 Germany. 968,742 3/1958 Germany.

DONLEY J. STOCKING, Primary Examiner.

HENRY F. RADUAZO, Examiner. 

1. A CENTRIFUGAL COMPRESSOR COMPRISING A HOUSING HAVING INLET AND OUTLET PORTIONS FOR THE PASSAGE OF REFRIGERANT VAPOR THROUGH THE COMPRESSOR, AN IMPELLER IN SAID HOUSING FOR COMPRESSING REFRIGERANT VAPOR FROM A RELATIVELY LOW SUCTION PRESSURE AT SAID INLET PORTION TO A RELATIVELY HIGHER PRESSURE AT SAID DISCHARGE PORTION DURING OPERATION OF THE COMPRESSOR, BEARING MEANS MOUNTING SAID IMPELLER FOR ROTATION DURING OPERATION OF SAID COMPRESSOR AND MOUNTING SAID IMPELLER SPACED FROM A PORTION OF SAID HOUSING TO DEFINE A GAP IN DIRECT COMMUNICATTION WITH SAID DISCHARGE PORTION, WHEREBY REFRIGERANT VAPOR AT SAID HIGHER PRESSURE PASSES INTO SAID GAP, MEANS FOR RETARDING FLOW OF SAID REFRIGERANT TO AT LEAST A PORTION OF SAID GAP, MEANS FOR PROVIDING LUBRICANT TO SAID BEARING MEANS AT A PRESSURE NORMALLY ABOVE SAID SUCTION PRESSURE, MEANS PROVIDING A COLLECTION CHAMBER IN SAID HOUSING BETWEEN AND IN FLUID COMMUNICATION WITH SAID GAP AND SAID BEARING MEANS, CONDUIT MEANS BETWEEN SAID CHAMBER AND A SEPARATE CHAMBER FOR MAINTAINING SAID CHAMBER AT A PRESSURE BELOW SAID LUBRICANT PRESSURE DURING OPERATON OF THE COMPRESSOR, AND MEANS COMMUNICATING WITH SAID INLET FOR MAINTAINING A PRESSURE IN SAID GAP BELOW SAID HIGHER PRESSURE TO REDUCE THE THRUST FORCE ON SAID IMPELLER, AND ABOVE THE PRESSURE IN SAID COLLECTION CHAMBER FOR ASSURING FLOW OF REFRIGERANT FROM SAID GAP INTO SAID CHAMBER AND SUBSTANTIALLY PREVENTING LEAKAGE OF SAID LUBRICANT INTO SAID GAP, WHEREBY REFRIGERANT MAY FLOW FROM SAID GAP INTO SAID CHAMBER AND LUBRICANT MAY FLOW FROM SAID BEARING MEANS INTO SAID CHAMBER. 